fbdev/viafb: Initialize fb_ops to fbdev I/O-memory helpers

Initialize the instance of struct fb_ops with fbdev initializer
macros for framebuffers in I/O address space. Set the read/write,
draw and mmap callbacks to the correct implementation and avoid
implicit defaults. Also select the necessary I/O helpers in Kconfig.

Fbdev drivers sometimes rely on the callbacks being NULL for a
default implementation to be invoked; hence requiring the I/O
helpers to be built in any case. Setting all callbacks in all
drivers explicitly will allow to make the I/O helpers optional.
This benefits systems that do not use these functions.

No functional changes.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230927074722.6197-46-tzimmermann@suse.de

drivers/video/fbdev/Kconfig

@@ -1240,6 +1240,7 @@ config FB_VIA
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_FOPS
 	select I2C_ALGOBIT
 	select VIDEO_NOMODESET
 	help

drivers/video/fbdev/via/viafbdev.c

@@ -2054,6 +2054,7 @@ static struct fb_ops viafb_ops = {
 	.owner = THIS_MODULE,
 	.fb_open = viafb_open,
 	.fb_release = viafb_release,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_check_var = viafb_check_var,
 	.fb_set_par = viafb_set_par,
 	.fb_setcolreg = viafb_setcolreg,
@@ -2065,6 +2066,7 @@ static struct fb_ops viafb_ops = {
 	.fb_cursor = viafb_cursor,
 	.fb_ioctl = viafb_ioctl,
 	.fb_sync = viafb_sync,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };